Automatic transmissions with several gear ratios that can be engaged without range change are widely known. From U.S. Pat. No. 5,106,352 a 6-gear automatic transmission is known, in which a simple transfer planetary gearset is arranged co-axially with a two-carrier, four-shaft main gearset made as a Ravigneaux planetary gearset and five shift elements are provided. In this, the transfer planetary gearset is made as a non-shiftable step-down stage with a sun gear fixed to a transmission housing. The output speed of which is slower than the speed of a drive input shaft of the automatic transmission and can be transferred via two clutches to two different elements of the main gearset, and one of the two elements can additionally be fixed relative to the transmission housing by a first brake. The input element of the main gearset, which can optionally be connected with the output element of the transfer planetary gearset or fixed relative to the transmission housing, will be referred to in what follows as the “first input element of the main gearset”. Correspondingly, the other input element of the main gearset will be called the “second input element of the main gearset” in what follows. The speed of the drive input shaft can be transferred by a third clutch to a third input element of the main gearset, and this third element can also be fixed relative to the transmission housing by a second brake. A fourth element of the main gearset forms the output element of the main gearset and is exclusively in fixed connection with a drive output shaft of the automatic transmission.
Several component arrangements alternative to this automatic transmission described in U.S. Pat. No. 5,106,352 are known, for example from U.S. Pat. No. 6,139,463 and DE 102 10 348 A1.
The unpublished German patent application DE 102 21 095.0 by the present Applicant describes developing the 6-gear automatic transmission known from U.S. Pat. No. 5,106,352, into a 7-gear automatic transmission. Compared with U.S. Pat. No. 5,106,352 the transfer planetary gearset is made as a simple, shiftable “positive” planetary gearset of double-planetary structure and an additional, sixth shift element is added. A carrier of the transfer planetary gearset forms the input element of the transfer planetary gearset in fixed connection with the drive input shaft of the automatic transmission. In contrast to U.S. Pat. No. 5,106,352 a sun gear of the transfer planetary gearset can be fixed relative to a transmission housing with the sixth shift element. Correspondingly, a ring gear of the transfer planetary gearset forms the output element of the transfer planetary gearset that can be connected with two different elements of the main gearset, and rotates at a speed slower than or equal to that of the drive input shaft. For this kinematic coupling of the individual gearset elements and shift elements, DE 102 21 095.0 discloses numerous different arrangement variants of the transmission components relative to one another.
JP 2001/182785 A describes further developing the 6-gear automatic transmission known from U.S. Pat. No. 5,106,352 into an 8-gear automatic transmission. Compared with U.S. Pat. No. 5,106,352, in this case the transfer planetary gearset is made as a simple, non-shifting “positive” planetary gearset of double-planetary structure and an additional, sixth shift element is added. A carrier of the transfer planetary gearset forms the input element of the transfer planetary gearset and is in fixed connection with the drive input shaft of the automatic transmission. A sun gear of the transfer planetary gearset is fixed relative to a transmission housing. Correspondingly, a ring gear of the transfer planetary gearset forms the output element of the transfer planetary gearset that can be connected with two different elements of the main gearset, and always rotates at a speed slower than or equal to that of the drive input shaft. Via the additional, sixth shift element compared with U.S. Pat. No. 5,106,352, the first input element of the main gearset—which can optionally be connected with the output element of the transfer planetary gearset or fixed relative to the transmission housing—can now optionally also be connected to the drive input shaft of the transmission. With regard to the spatial arrangement of the shift elements relative to one another and relative to the planetary gearsets, it is proposed in JP 2001/182785 A to arrange the two shift elements, by way of which the first and second input elements of the main gearset can be connected with the ring gear of the transfer planetary gearset, together with the additional, sixth shift element compared with U.S. Pat. No. 5,106,352, as a single structural group axially between the transfer planetary gearset and the main gearset. The (fifth) shift element already known from U.S. Pat. No. 5,106,352, by which the drive input shaft can be connected to the third input element of the main gearset, is arranged on the opposite side of the main gearset to this structural group, i.e., on the side of the main gearset facing away from the transfer planetary gearset. In addition, JP 2001/182785 A proposes to arrange the additional, sixth shift element compared with U.S. Pat. No. 5,106,352 within the structural group spatially radially over the shift element by way of which the first input element of the main gearset can be connected to the ring gear of the transfer planetary gearset.
In the unpublished German patent application DE 103 18 565.8 by the present applicant, an improved arrangement of the component of the 8-gear automatic transmission known from JP 2001/182785 A is described. In order to have to make only comparatively few design changes compared to the basic design of the 6-gear automatic transmission according to U.S. Pat. No. 5,106,352 upon which these variants are modelled, in DE 103 18 565.8 it is proposed to maintain the spatial position of the transfer planetary gearset, the Ravigneaux main gearset and the first five shift elements relative to one another in the transmission housing, known from the 6-gear automatic transmission, and to arrange the additional, sixth shift element compared with U.S. Pat. No. 5,106,352 in the transmission housing on the side of the transmission facing a drive engine, spatially between a transmission housing wall on the drive input side and a first shift element, by which the output element of the transfer planetary gearset can be connected with the second input element of the main gearset, but spatially also between the transmission housing wall on the drive input side and the transfer planetary gearset. The additional, sixth shift element compared with U.S. Pat. No. 5,106,352 is thus arranged on the side of the transfer planetary gearset facing away from the main gearset.
The purpose of the present invention is to further develop the multi-stage automatic transmission described in JP 2001/182785 A and DE 103 18 565.8 to include eight forward gear ratios, and to provide alternative arrangements of components for the planetary gearsets and the six shift elements.